1. Field of the Invention
The present invention relates to a water-based ink, and more particularly to a water-based ink which can be suitably used for a water-based ink for inkjet recording.
2. Discussion of the Related Art
Recently, pigment dispersions have been used as colorants in order to meet the demands of light fastness and water resistance for water-based inks.
Polymeric dispersing agents, surfactants and the like have been used in a pigment dispersion used for writing utensils and usual inks. However, when this pigment dispersion is used for a water-based ink, water resistance and light fastness of the printed matter are not satisfactory. Also, when the pigment dispersion is used for a water-based ink for inkjet recording, storage stability and discharging property of ink droplets are not satisfactory.
In order to eliminate the above defects, there have been proposed an ink comprising an AB-type block polymer (Japanese Patent Laid-Open No. Hei 4-227668); an ink comprising an AB-type graft copolymer having a hydrophilic segment and a hydrophobic segment, the main chain of which is different from the side chain thereof (Japanese Patent Laid-Open No. Hei 10-87768); and the like.
Inkjet printing system is a printing system comprising directly jetting ink droplets from very fine nozzles, and depositing the ink droplets on a recording medium, to give characters and images. This system is advantageous in that not only the used device shows a low level of noise and has excellent operability, but also the coloration is facilitated and plain paper can be used as a recording medium. Especially, full color printing technique is advantageous in that vivid printed images having high chroma can be obtained when using a dye having ample color toning as compared to other printing systems.
Especially in the recent years, with the widespread of digital cameras, printed images having a high printed density, which are sharp like a photograph have been required.
In addition, various proposals have been made in order to improve weather resistance such as light fastness and water resistance of an ink. The dye is attractive in that it has vivid colors and its kinds are abundant. However, there are some defects in the dye such that discoloration or fading is caused in accordance with the passage of time, and that water resistance is low as to a water-soluble dye. On the other hand, there are some pigments which are excellent in light fastness, such as inorganic pigments such as carbon black, and metal-containing organic pigments such as copper phthalocyanine pigments. However, there is a defect in many of organic pigments such that discoloration or fading is caused in accordance with the passage of time.
In addition, color printed images are formed by a plurality of inks in general. If even one of the color inks is poor in weather resistance, the hue of printed images changes in accordance with the passage of time, so that the quality of its printed images is deteriorated. In view of the above, even more excellent weather resistance has been demanded for inks used for color printed images.
In order to improve weather resistance of the ink, there has been proposed to add an ultraviolet ray absorbent, a photostabilizer, an antioxidant, an ozone-deterioration preventive, or the like to the ink. However, since many of those components are oil-soluble, they cannot be used for an aqueous ink in an amount sufficient for imparting weather resistance.
As a means for improving weather resistance of an aqueous ink, there has been proposed a process comprising adding to an aqueous dispersion, polymer particles containing an ultraviolet ray absorbent or a photostabilizer, or polymer particles prepared by incorporating an ultraviolet ray absorbent or a photostabilizer to a polymer skeleton by copolymerization (Japanese Patent Laid-Open No. Hei 11-12519). However, there arise some defects in this process that scorching on the printer head of the inkjet printer is caused, and that clogging in the internal of its nozzles is likely to be caused.
An object of the present invention is to provide a water-based ink which gives clear printed characters, especially has a high printed density and no crookedness of a printed matter, and also has excellent weather resistance.
Another object of the present invention is to provide a water-based ink for inkjet recording which would not cause scorching on the printer head of the inkjet printer and clogging in the internal of the nozzle of the inkjet printer.
These and other objects of the present invention will be apparent from the following description.